INTRO(4N)INTRO(4N)NAMEnetworking - introduction to networking facilities
SYNOPSIS
#include <sys/socket.h>
#include <net/route.h>
#include <net/if.h>
DESCRIPTION
This section briefly describes the networking facilities available in
the system. Documentation in this part of section 4 is broken up into
three areas: protocol families (domains), protocols, and network
interfaces. Entries describing a protocol family are marked ``4F,''
while entries describing protocol use are marked ``4P.'' Hardware
support for network interfaces are found among the standard ``4''
entries.
All network protocols are associated with a specific protocol family.
A protocol family provides basic services to the protocol
implementation to allow it to function within a specific network
environment. These services may include packet fragmentation and
reassembly, routing, addressing, and basic transport. A protocol
family may support multiple methods of addressing, though the current
protocol implementations do not. A protocol family is normally
comprised of a number of protocols, one per socket(2) type. It is not
required that a protocol family support all socket types. A protocol
family may contain multiple protocols supporting the same socket
abstraction.
A protocol supports one of the socket abstractions detailed in
socket(2). A specific protocol may be accessed either by creating a
socket of the appropriate type and protocol family, or by requesting
the protocol explicitly when creating a socket. Protocols normally
accept only one type of address format, usually determined by the
addressing structure inherent in the design of the protocol
family/network architecture. Certain semantics of the basic socket
abstractions are protocol specific. All protocols are expected to
support the basic model for their particular socket type, but may, in
addition, provide non-standard facilities or extensions to a mechanism.
For example, a protocol supporting the SOCK_STREAM abstraction may
allow more than one byte of out-of-band data to be transmitted per out-
of-band message.
A network interface is similar to a device interface. Network
interfaces comprise the lowest layer of the networking subsystem,
interacting with the actual transport hardware. An interface may
support one or more protocol families and/or address formats. The
SYNOPSIS section of each network interface entry gives a sample
specification of the related drivers for use in providing a system
description to the config(8) program. The DIAGNOSTICS section lists
messages which may appear on the console and/or in the system error
log, /usr/adm/messages (see syslogd(8)), due to errors in device
operation.
PROTOCOLS
The system currently supports the DARPA Internet protocols and the
Xerox Network Systems(tm) protocols. Raw socket interfaces are
provided to the IP protocol layer of the DARPA Internet, to the IMP
link layer (1822), and to the IDP protocol of Xerox NS. Consult the
appropriate manual pages in this section for more information regarding
the support for each protocol family.
ADDRESSING
Associated with each protocol family is an address format. The
following address formats are used by the system (and additional
formats are defined for possible future implementation):
#define AF_UNIX 1 /* local to host (pipes, portals) */
#define AF_INET 2 /* internetwork: UDP, TCP, etc. */
#define AF_IMPLINK 3 /* arpanet imp addresses */
#define AF_PUP 4 /* pup protocols: e.g. BSP */
#define AF_NS 6 /* Xerox NS protocols */
#define AF_HYLINK 15 /* NSC Hyperchannel */
ROUTING
The network facilities provided limited packet routing. A simple set
of data structures comprise a ``routing table'' used in selecting the
appropriate network interface when transmitting packets. This table
contains a single entry for each route to a specific network or host.
A user process, the routing daemon, maintains this data base with the
aid of two socket-specific ioctl(2) commands, SIOCADDRT and SIOCDELRT.
The commands allow the addition and deletion of a single routing table
entry, respectively. Routing table manipulations may only be carried
out by super-user.
A routing table entry has the following form, as defined in
<net/route.h>;
struct rtentry {
u_long rt_hash;
struct sockaddr rt_dst;
struct sockaddr rt_gateway;
short rt_flags;
short rt_refcnt;
u_long rt_use;
struct ifnet *rt_ifp;
};
with rt_flags defined from,
#define RTF_UP 0x1 /* route usable */
#define RTF_GATEWAY 0x2 /* destination is a gateway */
#define RTF_HOST 0x4 /* host entry (net otherwise) */
#define RTF_DYNAMIC 0x10 /* created dynamically (by redirect) */
Routing table entries come in three flavors: for a specific host, for
all hosts on a specific network, for any destination not matched by
entries of the first two types (a wildcard route). When the system is
booted and addresses are assigned to the network interfaces, each
protocol family installs a routing table entry for each interface when
it is ready for traffic. Normally the protocol specifies the route
through each interface as a ``direct'' connection to the destination
host or network. If the route is direct, the transport layer of a
protocol family usually requests the packet be sent to the same host
specified in the packet. Otherwise, the interface is requested to
address the packet to the gateway listed in the routing entry (i.e. the
packet is forwarded).
Routing table entries installed by a user process may not specify the
hash, reference count, use, or interface fields; these are filled in by
the routing routines. If a route is in use when it is deleted
(rt_refcnt is non-zero), the routing entry will be marked down and
removed from the routing table, but the resources associated with it
will not be reclaimed until all references to it are released. The
routing code returns EEXIST if requested to duplicate an existing
entry, ESRCH if requested to delete a non-existent entry, or ENOBUFS if
insufficient resources were available to install a new route. User
processes read the routing tables through the /dev/kmem device. The
rt_use field contains the number of packets sent along the route.
When routing a packet, the kernel will first attempt to find a route to
the destination host. Failing that, a search is made for a route to
the network of the destination. Finally, any route to a default
(``wildcard'') gateway is chosen. If multiple routes are present in
the table, the first route found will be used. If no entry is found,
the destination is declared to be unreachable.
A wildcard routing entry is specified with a zero destination address
value. Wildcard routes are used only when the system fails to find a
route to the destination host and network. The combination of wildcard
routes and routing redirects can provide an economical mechanism for
routing traffic.
INTERFACES
Each network interface in a system corresponds to a path through which
messages may be sent and received. A network interface usually has a
hardware device associated with it, though certain interfaces such as
the loopback interface, lo(4), do not.
The following ioctl calls may be used to manipulate network interfaces.
The ioctl is made on a socket (typically of type SOCK_DGRAM) in the
desired domain. Unless specified otherwise, the request takes an
ifrequest structure as its parameter. This structure has the form
struct ifreq {
char ifr_name[16]; /* name of interface (e.g. "ec0") */
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
short ifru_flags;
int ifru_metric;
} ifr_ifru;
#define ifr_addr ifr_ifru.ifru_addr /* address */
#define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
#define ifr_flags ifr_ifru.ifru_flags /* flags */
#define ifr_metric ifr_ifru.ifru_metric /* routing metric */
};
SIOCSIFADDR
Set interface address for protocol family. Following the
address assignment, the ``initialization'' routine for the
interface is called.
SIOCGIFADDR
Get interface address for protocol family.
SIOCSIFDSTADDR
Set point to point address for protocol family and interface.
SIOCGIFDSTADDR
Get point to point address for protocol family and interface.
SIOCSIFBRDADDR
Set broadcast address for protocol family and interface.
SIOCGIFBRDADDR
Get broadcast address for protocol family and interface.
SIOCSIFFLAGS
Set interface flags field. If the interface is marked down, any
processes currently routing packets through the interface are
notified; some interfaces may be reset so that incoming packets
are no longer received. When marked up again, the interface is
reinitialized.
SIOCGIFFLAGS
Get interface flags.
SIOCSIFMETRIC
Set interface routing metric. The metric is used only by user-
level routers.
SIOCGIFMETRIC
Get interface metric.
SIOCGIFCONF
Get interface configuration list. This request takes an ifconf
structure (see below) as a value-result parameter. The ifc_len
field should be initially set to the size of the buffer pointed
to by ifc_buf. On return it will contain the length, in bytes,
of the configuration list.
/*
* Structure used in SIOCGIFCONF request.
* Used to retrieve interface configuration
* for machine (useful for programs which
* must know all networks accessible).
*/
struct ifconf {
int ifc_len; /* size of associated buffer */
union {
caddr_t ifcu_buf;
struct ifreq *ifcu_req;
} ifc_ifcu;
#define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
#define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
};
SEE ALSOsocket(2), ioctl(2), intro(4), config(8), routed(8C)4.2 Berkeley Distribution June 1, 1986 INTRO(4N)
